1. Field of the Invention
The present application relates to processing audio signals containing noise, particularly for auditory prostheses.
2. Related Art
Auditory prostheses include any acoustic or electrical auditory prostheses, such as hearing aids, bone anchored hearing aids, middle ear implants, intracochlear implants, brain stem implants, implanted acoustic prostheses or any combination of these, for example prostheses providing combined electrical and acoustic stimulation. For those prostheses having an external part and an implanted part, the external part may be continuously, intermittently or occasionally in communication with the implanted part.
Auditory prostheses require, as an input, an electrical signal corresponding to an audio signal for processing in the device. This input is most commonly provided by a microphone. For example, a conventional cochlear implant consists of an external part containing a microphone, a sound processor and a transmitter, and an internal part which contains a receiver/stimulator device and an electrode array. Sound enters the microphone, which outputs a corresponding electrical signal to the sound processor, which in turn codes the sound using one of many possible processing strategies. The coded signal is passed to the transmitter, which sends it to the implanted receiver/stimulator unit. The receiver/stimulator then sends the corresponding stimuli to the appropriate electrodes, so as to provide a percept of hearing for a user.
A significant problem for users of auditory prostheses is listening to a target signal in the presence of noise, such as when talking on the phone, or in restaurants, sports stadiums, supermarkets, and the like. One major source of this problem is that a hearing impaired person has a much smaller range of perceivable sounds than a normal hearing person. This perceivable range of sounds is known as the dynamic range.
One way existing systems combat this problem is by automatically turning down the gain of the system in the presence of noise. By turning down the gain of the system the processor can lower the noise level such that it is mapped to the lower end of the recipient's dynamic range. An example of such an algorithm is disclosed in U.S. Pat. No. 6,151,400, and reproduced in part as FIG. 10.
The problem with such algorithms is that while they turn down the noise level, they also turn down the level of the target signal. This means that while the user may hear less noise, the target signal also becomes more difficult to hear.